For articles A, B, C, and D, a 1600 pound force would produce displacements of 4.6, 4.8, 5.5, and 3.6 inches, respectively. These deflections are still greater than those obtained in the Urethane-filled test articles, and the stiffening effect of the Urethane is even is even greater than accounted for by the theoretical analysis above. In order to more carefully examine this issue, a three-dimensional finite element analysis would be required, which is beyond the scope of the current study.

This ultimate failure load Is approximately 12.000 pounds for all four test articles, much greater than the 1600 pound force applied to the test articles.

            Figure 3 and 4 indicate the importance of the Poisson ratio of the in-fill material. As the Poisson ratio approaches (1/2), the stiffness and strength